Hi there not sure how far you have got but first of all you need to take out the two screws in the back light .Then ease the back light up a little then it should come away ..You will then see the bulb holder (black rubber outer case) You will find it's very tight and hard to get off .
Be carfull ..if and when you get it off replace the bulb but before you put it back together put a little grease /oil on the rubber then it will be easer to remove the next time .. Chas